A commercially available in vitro model of human conducting airways (EpiAirway) has been developed and utilized for a variety of basic research and industry drug delivery applications. However, the model has not been formally validated for toxicology applications in drug development and risk assessment. The goal of the present grant proposal is to validate the EpiAirway in vitro human airway model for these purposes following Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) and European Center for the Validation of Alternative Methods (ECVAM) guidelines. Experiments will be performed to determine in vitro responses of the EpiAirway model after treatment with 20 chemicals of known in vivo conducting airway toxic potentials. Test chemicals will be chosen from those with permissible exposure limits (PELs) established by Occupational Safety and Health Administration (OSHA) based upon in vivo human and animal inhalation data. In vitro endpoints in the EpiAirway model will be cytotoxicity as measured by the MTT and ToxiLight cytotoxicity assays, and inflammatory cytokine/chemokine (interleukin-8, interleukin 6 and granulocyte macrophage stimulating factor) production as measured by enzyme linked immunosorbant assays. The entire set of experiments will be repeated two separate times. The data will then be statistically analyzed to determine intralaboratory reproducibility and interlaboratory transferability. The in vitro cytotoxicity and cytokine/chemokine production data will be correlated with in vivo (PELs) established for the test chemicals by OSHA. Finally, the data will be statistically evaluated to produce a prediction model for converting in vitro cytotoxicity results into a prediction of in vivo PELs. These Phase I goals constitute the prevalidation process for establishing the feasibility of proceeding to full formal validation. Milestones for advancement to Phase II are acceptable reproducibility, interlaboratory transferability of protocols and development of an acceptable prediction model. In Phase II, formal validation studies will be conducted following ICCVAM guidelines. The number and types of test compounds and formulations will be expanded and tested in blinded trials in 4 independent laboratories. The study results will then be submitted for independent assessment and regulatory acceptance. [unreadable] [unreadable]